Men and women are consistently found to differ in their performance on spatial relationship tasks. The result of this sex difference is assumed to be differential mathematical abilities and the reduced participation of women in occupations that require quantitative abilities and analytical reasoning. The source of the sex difference in spatial skills has been widely discussed and debated in recent years. Biological explanations -- genetics, hormones, rate of maturation, and differential brain lateralization -- have been popular but remain unproved. Environmental explanations have focused largely on the influence of sex role labeling of spatial tasks and on differential practice through participation in "spatial activities." In this proposal, a specific mechanism -- motor activity -- is suggested as the behavioral mediator for the differential development of spatial skills in males and females. Decades ago, Piaget and Inhelder proposed that spatial perceptions were directly related to sensorimotor activity, but no empirical studies have been conducted to test this hypotheses. A recent finding that play with masculine sex-typed toys is associated with higher levels of motor activity and more vigorous play for both boys and girls than is play with other types of toys suggests that early self-selection of sex-typed toys and activities may be contributing to higher motor activity in boys as compared to girls. If physical activity is a factor in the development of spatial skills, then boys would be expected to perform better than girls on spatial tasks. In the proposed study, a group of preschool children whose toy preferences and motor activity levels were assessed when they were toddlers will be tested for spatial relations skills in order that the relationship among level of motor activity, sex-typed play, and spatial abilities in young children can be directly evaluated. It is hypothesized that levels of play with masculine sex-typed toys is associated with high motor activity and, in turn, with enhanced spatial relations skills.